1. Field of the Invention
The present invention relates to an integrated circuit packaging technology and in particular to a flip chip packaging technology.
2. Description of the Related Art
The flip chip package is the most space efficient package for very large scale integrated (VLSI) circuits. Flip chip technology is compatible with a variety of circuit board types, including ceramic substrates, printed wiring boards, flexible circuits, and silicon substrates. A flip chip is generally a monolithic semiconductor device, such as an integrated circuit (IC), having bead-like terminals formed on one of its surfaces. The terminals, usually in the form of solder bumps, serve to both secure the flip chip to a circuit board and electrically interconnect the chip circuitry to a conductor pattern formed on the circuit board.
In a flip chip package, an integrated circuit (IC) device usually has a plurality of bond pads distributed over the surface of the device in a rectangular array. These bond pads are used to connect the IC device to the electrical paths on a printed circuit board (PCB). A ball shaped solder bump is formed on each of the bond pads of the IC device. The IC device and the PCB are positioned so that the solder bumps contact the electrical paths on the PCB, and the assembly is heated to reflow the solder, forming electrical and mechanical bonds between the IC device and the PCB.
Erickson, in U.S. Pat. No. 6,180,265, discloses a method for converting an aluminum wire bond to a flip chip solder bump pad, so as to enable an IC device originally configured for wire-bonding attachment to be mounted using a flip chip attachment technique.
Chittipeddi et al., in U.S. Pat. No. 6,187,658 and in U.S. Pat. No. 6,087,732, discloses a method of forming a bond pad for flip chip package integrating the package process with the semiconductor manufacturing process.
The bond pads on the IC device are typically aluminum or an aluminum-base alloy for various known processing and performance-related reasons. FIG. 1A shows a sketch cross-section of a portion of the conventional flip chip package. As well, the cross-section of the entire structure of the conventional flip chip package is shown in FIG. 4. It is understood that chip 100 is conventionally provided with bond pads 102 and solder bumps 104. In order to clearly illustrate the structure of the flip chip package, only one bond pad 102 and one solder bump 104 is shown in the figure. Heat is usually produced during operation of the IC device, causing the expansion of the bond pad 100 and the PCB 106.
However, the thermal expansion coefficient of the bond pad 102 is very different from that of the PCB 106. As shown in FIG. 1B, the structure of the flip chip package subjected to the thermal stress is distorted. Thus, the solder bump 104 easily peels off.